It's going to be difficult beat the ~$50 price of something like the Thermochron 4K. I guess if you need the capabilities of the 8K version, you'll double the price. The main issue in getting something cheaper is getting something that doesn't require $200 of your time to assemble and deploy. It's also going to be hard the beat the ruggedness of the iButton with cheaper solutions.

I would suggest looking at something like a disposable cold chain tag. There are several companies that make them, but Freshliance is readily available through common retailers and on-line stores and can be